Field of the Invention
The present invention relates to an optical system and an image pickup apparatus including the same, which are suitable for, for example, an image pickup optical system used in an image pickup apparatus such as a digital still camera, a digital video camera, a television (TV) camera, a monitoring camera, a silverhalide film camera, or the like.
Description of the Related Art
It is desired that an image pickup optical system used in an image pickup apparatus retain, during focusing, reduced aberration variation and enhanced optical performance at any object distance, and have compact and light-weight focus lens units, which facilitate high-speed focusing. Focus types typically employed, for the image pickup optical system include an inner focus type where part of the lens units in the image pickup optical system works for focusing. The inner focus type more easily enables downsizing and reduction in weight of the lens units for focusing (focus lens units) and facilitates high speed focusing, compared with some other focus types where all the components of the image pickup optical system are required to be moved.
In general, in the image pickup optical system, a shorter photographing distance develops various aberrations more. Especially, when an object being photographed is at so close range as an image-to-object ratio is approximately 1, various aberrations are significantly increased, resulting in deteriorated optical performance. A photographing lens primarily used for photographing the object at short distance is known as “macro lens”. In Japanese Patent Application Laid-Open No 2006-153942 and Japanese Patent Application Laid-Open No 2011-048232, there is disclosed an image pickup optical system of a floating type where two or more of the lens units are configured to move during the focusing to reduce the variations in aberrations due to the focusing.
In Japanese Patent Application Laid-Open No. 2006-153942, there is disclosed an image pickup optical system consisting of our lens units, namely, a first positive lens unit, a second negative lens unit, a third positive lens unit, and a fourth negative lens unit arranged in the stated order from the object side to the image side. For focusing from an object at infinity to an object at short distance, the second lens unit is moved toward the image side while the third lens unit is moved toward the object side.
In Japanese Patent Application Laid-Open No. 2011-048232, there is disclosed an image pickup optical system consisting of six lens units, namely, a first positive lens unit, a second negative, lens unit, a third positive lens unit, a fourth positive lens unit, a fifth negative lens unit, and a sixth positive lens unit arranged in the stated order from the object side to the image side. For focusing from an object at infinity to an object at short distance, at least three lens units are moved.
In general, in focusing of the inner focus and the floating type, it is important to appropriately set the refractive power and the configuration of each of the lens units of the image pickup optical system. Especially, it is important to appropriately select which of the plurality of the lens units are to be moved as floating lens elements.
Unless those factors are appropriately specified, there arise difficulties in making the focus lens units more compact and lighter in weight, reducing the variations in aberrations during the focusing, and obtaining enhanced optical performance for focusing at any object distance from an object at infinity to an object at short distance.